T. Radil

Temporal integration in sensorimotor synchronization

The concept of a temporal integration process in the timing mechanisms in the brain, postulated on the basis of experimental observations from various paradigms (for a review see P

Pre-Attentive Discriminability of Sound Order as a Function of Tone Duration and Interstimulus Interval: A Mismatch Negativity Study

oUppel, 1978), has been explored in a sensorimotor synchronization task. Subjects synchronized their finger taps to sequences of auditory stimuli with interstimulus-onset intervals (ISIs) between 300 and 4800 msec in different trials. Each tonal sequence consisted of 110 stimuli; the tones had a frequency of 500 Hz and a duration of 100 msec. As observed previously, response onsets preceded onsets of the stimuli by some tens of milliseconcls for ISIs in the range from about 600 to 1800 msec. For ISIs longer than or equal to 2400 msec, the ability to time the response sequence in such a way that the response 5 were placed right ahead of the stimuli started to break clown, i.e., the task was fulfilled by reactions to the stimuli rather than by advanced responses. This observation can he understood within the general framework of a temporal integration puce 55 that is supposed to have a maximal capacity (integration interval) of approximately 3 sec. Only if successive stimuli fall within one integration period, can motor programs be initiated properly by a prior stimulus and thus lead to an appropriate synchronization between the stimulus sequence and corresponding motor acts.

EEG changes related to one-dimensional hand-tracking

The present study addressed the pre-attentive processing of sound order. Event-related potentials were recorded from reading subjects while they were presented with pairs of two tones differing from each other in frequency (1000 vs. 1500 Hz). The within-pair (silent) interstimulus interval (ISI) was, in separate blocks, varied between 0 and 245 ms to determine the minimum separation in time needed for detecting the reversed order of the two frequencies. In standard tone pairs (p = 0.9), the frequencies were in an ascending order, whereas in the deviant pairs (p = 0.1), their order was reversed. Tone durations of 5 and 20 ms were employed in separate experiments. With the 20-ms stimulus duration, the change-specific mismatch negativity (MMN) component was elicited with all within-pair ISIs employed (0, 10, 30, 90 ms). With the 5-ms stimulus duration, however, MMN was elicited only with the 245-ms ISI but not with 95-ms or shorter ISIs. These results show that increased stimulus duration considerably improves perceiving the order of two tones at the pre-attentive level. They also indicate that the accuracy of the processing of temporal information can be probed with MMN. This finding, together with the fact that MMN elicitation does not require the subject’s voluntary attention, suggests that MMN might be used in the assessment of temporal processing deficits in clinical disorders in which patients are not motivated or able to give their verbal or motor response.

Extralemniscal co-activation is not indispensable for behavioral detection of auditory stimuli

Central and occipital EEGs were recorded during one-dimensional eye-hand tracking in humans. A negative slow potential shift followed the commitment of tracking errors at electrode O1 and their correction both at O1 and C3. Error commitments were also followed by a relative decrease in alpha and beta-band power at O1, whereas their corrections followed a decrease in beta-band power at O2 and C3.

Auditory-evoked responses influenced by presence or absence of EEG alpha activity and actual cognitive state

Thresholds for triggering summed auditory evoked responses (ERs) were measured in non-auditory (= extralemniscal--EL) nuclei receiving direct auditory projections from the lateral lemniscus. Primary EL ERs with onset latency of 3-6 ms reflecting activation of direct EL projections of lemniscal auditory nuclei were registered in caudal pontine reticular nucleus (CPRN), in deep layers of superior colliculus (SC) and in ventromedial hypothalamus (VMH). Secondary EL ERs (waves of EL ERs with onset latency above 10 ms) reflecting diffuse auditory EL co-activation of the brain, were registered besides the above mentioned nuclei also in the medial amygdala (MA). Threshold sound intensities for evoking primary EL ERs in CPRN, SC and VMH, for secondary EL ERs in all extralemniscal nuclei tested, and for conditioned avoidance behavior in a two-way shuttle box, were compared mutually. There were no significant mutual differences among thresholds for inducing secondary EL ERs in all EL nuclei tested. Thresholds for evoking secondary EL ERs were lower than those for evoking primary EL ERs in deep layers of the SC, equaled to thresholds for primary EL ERs in the VMH and were higher than thresholds for primary EL ERs in the CPRN. The results suggest that auditory EL projections into SC and/or VMH (but not into CPRN) might represent the primary triggering source for secondary EL ERs in various extralemniscal nuclei. Although conditioning lowered the threshold intensities for inducing secondary EL ERs, the threshold sound intensity for triggering conditioned behavior was lower than the threshold for secondary EL ERs.(ABSTRACT TRUNCATED AT 250 WORDS)

Gamma activity in the piriform cortex and behavioral thresholds for electrical stimulation in the olfactory bulb

The presence or absence of alpha activity in occipital EEG was detected automatically. Auditory-evoked responses (AERs) related to these two brain states and at the same time to different perceptual-cognitive situations (passive listening, discrimination between two tones and pressing the button accordingly similar discrimination without motor reaction) were analyzed and compared statistically. The main result was that during the alpha state (and not during the non-alpha state, when EEG was desynchronized), the amplitudes of N1, P1 waves and peak-to-peak amplitudes N1-P2 were higher during passive listening to stimuli in comparison with the active perceptual-cognitive states mentioned. No differences in latencies of AERs were found.